This invention relates to a power transmission device for use in a vehicle and the like.
A drive power distribution control device for a vehicle is disclosed in Japanese Patent Laid Open No. 204827/1989. A transfer case is disclosed in Japanese Patent Laid Open No. 97425/1988. The inventions described in these publications are both directed to a transfer for distributing drive power generated by an engine to front and rear wheels in an automobile of a four-wheel drive type. The transfer includes a limit slip differential (LSD) mechanism. The limit slip differential mechanism disclosed in the former publication comprises a multiple-disk clutch actuated by a hydraulic actuator which is supplied with a hydraulic pressure from an oil pump driven by the engine. The limit slip differential mechanism disclosed in the latter publication comprises an electromagnetic multiple-disk clutch.
In the transfer described in each publication, lubricating points at a bearing section and a power transmitting section such as a gear engagement portion and a clutch portion are distributed along an axial direction. In order to supply oil to those widespread lubricating points, use has been made of a method of directing the oil through an oil gutter to each section and making the oil flow down. With this method, the oil is splashed by centrifugal force. This results in insufficient lubrication.
The former publication teaches to carry out forced lubrication wherein the oil is circulated from the oil pump through an oil path formed in a shaft to each lubricating point. In this event, the engine is inevitably suffered from power loss due to necessity of pressurization of the lubricating oil and due to an increased weight resulting from installation of the oil pump. Consequently, fuel efficiency is decreased.
The latter publication describes a function of eliminating abrasion dust which is produced from a friction plate or a gear engagement portion and scattered in the oil. Specifically, the abrasion dust is attracted by an electromagnet and removed from the oil. However, the splashed oil directly strikes the electromagnet. In this event, the abrasion dust once attracted may possibly be returned back into the oil. Furthermore, since the electromagnet and the splashed oil are brought into contact with each other for a very short time interval, the oil has little effect in cooling the electromagnet.